In the coming year major attention will be given to dietary iron absorption. The interaction of blocking and enhancing substances in the diet as they determine the availability of nonheme iron will be examined. Attention will be given to various ways of more effectively fortifying the diet. In respect to internal iron metabolism, the significance of plasma ferritin and its possible role in regulation of iron exchange will be examined. Studies of erythropoiesis will focus on the proliferative potential of the erythroid marrow as studied by colony formation in vitro and on studies of the biochemical mechanism of erythropoietin action in in vitro models. Studies of granulopoiesis will focus on the quantitation of the marrow granulocyte production, utilizing methods developed which determine marrow granulocyte turnover. These measurements will be applied to studies in the dog and to granulocyte disorders in man. Particular attention will be given to the effect of the spleen on neutrophil turnover and distribution.